Nice early Jungle Carbine! That probably explains the 3 digit number. (It might even be a 'Trial #').

Mine was built by Fazakerly in 1947, so, it has the later metal forearm 'cap' and a four digit serial number.

The British did not issue extra magazines with Lee-Enfield rifles. They reloaded with 5-round 'Chargers' carried in cloth bandoliers.

My magazine has a matching serial number on the bottom of the magazine.
I don't think the war time No. 5 rifles had the magazines serial numbered.

I believe your canvass gear is all U.S. items. The sling is like the one the CMP sent with my M1 Garand.

Like 'Littlejohn' said, the "England" was to comply with U.S. Customs law. The "BNP Proofs" were to comply with British law for civilian sales.

p.s. The pressure test is 18.5 "Long Tons" per square inch.